The invention relates to a method for fabricating a thermoelectric converter.
DE 39 35 610 A1 describes a Peltier cooler having an interconnection of n- and p-doped semiconductor segments which are connected together with the aid of metal bridges. In this case, the metal bridges are applied on Al2O3 substrates and the semiconductor segments in the case of one of these substrates are vapor-deposited onto the metal bridges present there. Peltier coolers of this type have a physical size in the centimeters range and cannot readily be miniaturized, with the result that the power density is very low. Furthermore, the Al2O3 substrates have a very low thermal conductivity, which impairs the effectiveness of such Peltier coolers.
The object of the present invention consists in developing a method for fabricating a thermoelectric converter of the type mentioned in the introduction which allows a higher integration level of the thermoelement cells and thereby enables the fabrication of thermoelectric components with a higher power density and in which cost-effective processes are used.
This object is achieved by means of a method having the features of claim 1. Subclaims 2 to 10 relate to advantageous developments of the method.
The method according to the invention is used to fabricate a thermoelectric converter having a plurality of series-connected thermoelement cells, which are connected in series with one another by means of a plurality of first electrical conductor tracks and each of which has a first body made of thermoelectric material of a first conduction type and a second body made of thermoelectric material of a second conduction type, which are connected to one another by means of a second electrical conductor track and which are arranged in a sandwich-like manner between a first and a second substrate wafer which is electrically insulating or has an electrically insulating layer.
In the method, the first electrical conductor tracks are formed on a main area of the first substrate wafer. The second electrical conductor tracks are produced on a main area of the second substrate wafer. In the case of at least one of the two substrate wafers, at least one layer made of thermoelectric material is applied on the same side on which the conductor tracks are produced. Said layer is patterned by means of photomask technology and etching in such a way that the first and second bodies of the thermoelement cells are produced.
After the processing of the two substrate wafers, the latter are joined together e.g. by means of thermocompression, soldering, adhesive bonding or anodic bonding to form a sandwich composite, in which the first and the second bodies are arranged between the two substrate wafers and are connected by means of the first and second electrical conductor tracks to form thermoelement cells connected in series.
In each case a first and a second body are connected on a first side by means of a first conductor track to form a thermoelement cell, which are connected in series with one another by means of the second conductor tracks on a second sidexe2x80x94opposite to the first sidexe2x80x94of the first and second bodies.
In a preferred embodiment for producing the first and second conductor tracks and the first and second bodies, firstly a first electrically conductive layer is applied to the main area of the first substrate wafer. A layer made of thermoelectric material is subsequently deposited onto said electrically conductive layer and a plurality of doped regions of the first conduction type and a plurality of doped regions of the second conduction type are then formed in said layer made of thermoelectric material.
The layer made of thermoelectric material is subsequently patterned by means of photomask technology and etching to form first and second bodies; i.e., after the patterning mutually isolated first and second bodies remain on the first electrically conductive layer.
After this process step, the first electrically conductive layer is patterned for example once again by means of photomask technology and etching to form first conductor tracks which each connect a first and a second body to one another on one side of the bodies, thereby producing a plurality of mutually isolated thermoelement cells.
However, the first electrically conductive layer can also be patterned to form first conductor tracks even before the application of the layer made of thermoelectric material.
Before, during or after these steps, a second electrically conductive layer is applied to the main area of the second substrate wafer and is subsequently patterned, for example, once again by means of photomask technology and etching to form second conductor tracks which connect the thermoelement cells in series with one another in the sandwich composite.
The two wafers are joined together to form the sandwich composite in the manner already specified further above.
In another preferred embodiment for producing the first and second conductor tracks and the first and second bodies, a first electrically conductive layer is applied to the main area of the first substrate wafer. That is followed by application of a first layer made of thermoelectric material, which is of the first conduction type, to the first electrically conductive layer.
This first layer made of thermoelectric material is subsequently patterned by means of photomask technology and etching in such a way that a plurality of mutually isolated first bodies are produced on the first electrically conductive layer.
After this process step, the first electrically conductive layer is patterned for example once again by means of photomask technology and etching to form first conductor tracks.
In this case, too, the first electrically conductive layer can, however, also be patterned to form first conductor tracks even before the application of the first layer made of thermoelectric material.
Before, during, or after these process steps, a second electrically conductive layer is applied to the main area of the second substrate wafer and a second layer made of thermoelectric material, which is of the second conduction type, is deposited on said second electrically conductive layer.
This second layer made of thermoelectric material is then patterned by means of photomask technology and etching in such a way that a plurality of mutually isolated second bodies are produced on the second electrically conductive layer.
The second electrically conductive layer is subsequently patterned to form second conductor tracks for example once again by means of photomask technology and etching.
The second electrically conductive layer can also be patterned to form second conductor tracks even before the application of the second layer made of thermoelectric material.
The two wafers are joined together to form a sandwich composite with thermoelement cells connected in series in the manner already specified further above.
In a further preferred embodiment for producing the first and second conductor tracks and the first and second bodies, a first electrically conductive layer is again applied to the main area of the first substrate wafer. That is followed by application of a first layer made of thermoelectric material, which is of the first conduction type, to the first electrically conductive layer.
A first layer made of thermoelectric material, which is of the first conduction type, is then deposited onto said first electrically conductive layer. This first layer is subsequently patterned by means of photomask technology and etching in such a way that a plurality of first bodies are produced on the first electrically conductive layer.
A second layer made of thermoelectric material, which is of the second conduction type, is then applied to these first bodies and to the free surfacexe2x80x94lying between the first bodiesxe2x80x94of the first electrically conductive layer. This second layer is subsequently patterned once again by means of photomask technology and etching in such a way that a plurality of second bodies are produced on the free surface of the first electrically conductive layer.
The first electrically conductive layer can be patterned to form first conductor tracks before or after the application of the first and second layer made of thermoelectric material.
Before, during or after these process steps, a second electrically conductive layer is applied to the main area of the second substrate wafer and is subsequently patterned to form second conductor tracks.
The two wafers are joined together to form a sandwich composite with thermoelement cells connected in series in this case once again in the manner already specified further above.
The particular advantage of the abovementioned methods is that processes of semiconductor technology can be used for fabricating the first and second conductor tracks and the first and second bodies. As a result, both the integration level of the thermoelement cells and the fabrication costs for thermoelectric converters can be considerably reduced. This last is due to the fact that conventional and established processes of semiconductor technology which are used for the mass production of semiconductor chips are employed.
The thermoelectric converters fabricated by the method according to the invention can advantageously be integrated in a simple manner together with elements of microelectronics and/or microsystems technology on one and the same chip.
With the method according to the invention, the first and the second bodies can be fabricated in a simple manner from multilayer systems comprising a multiplicity of thin layers having a different material composition. As a result, the performance of thermoelectric converters can advantageously be increased by the use of layer sequences that are exactly coordinated with one another.